Solvents such as hexane and toluene and components such as tetrahydrofuran and titanium tetrachloride are utilized in a number of chemical processes such as processes for producing the catalysts utilized in the polymerization of olefins.
It has been found that without solvent recovery and recycle the process for producing the catalyst may not be economically feasible or environmentally viable. Heretofore, a batch fractionation process was suggested for recovering the solvents and other components. However, the interaction between tetrahydrofuran (THF) and titanium tetrachloride (TiCl.sub.4) in a batch fractionator was unknown. Moreover, it has been determined that recovered toluene must be virtually free of THF in order to be reusable in a process for the production of an olefin polymerization catalyst.
Furthermore, studies have shown that it is difficult, if not impossible, to completely separate THF and hexane by straight distillation in view of the similar boiling points of THF and hexane. However, it has been observed (and incorporated into the process of the present invention) that complexes of TiCl.sub.4 and THF are insoluble in hexane even at room temperature. Accordingly, any buildup of THF in the hexane can be treated by adding TiCl.sub.4 and then filtering the liquid to remove the resulting solid precipitatable complex.
U.S. Pat. No. 4,588,704 describes a method of combining suitable portions of organic solvent or diluent which has been contacted with organoaluminum halide and titanium halide and washed at least once with water without adverse reactions or the excessive production of precipitation or gels and the organic phase of the diluent can subsequently be separated from the water phase for further purification and recycle into the process for production of polymerization catalyst.
U.S. Pat. No. 4,683,215 describes a process for removing one or more contaminants of the formula TiCl.sub.3 OR, in which R is an alkyl or aryl group, from a liquid phase comprising TiCl.sub.4, wherein the contaminants are reacted with an organic halide R'COCl in which R' is an aryl or alkyl group, to precipitate an addition complex of the formula nTiCl.sub.4.R'COOR in which n is a number of from 0.3 to 3.0 and the precipitated complex is separated from the liquid phase.
As will be described in greater detail hereinafter, the method and apparatus of the present invention utilize the presence of a complexing or precipitating agent, such as TiCl.sub.4, in a mother liquor to create precipitatable complexes of THF, such as TiCl.sub.4.C.sub.4 H.sub.8 O or TiCl.sub.4.2C.sub.4 H.sub.8 O, which are then precipitated from the mother liquor. Also, it has been determined that such precipitation is enhanced by cooling the mother liquor containing the precipitatable complexes. If required, complexing agent can be added to the mother liquor to promote formation of precipitatable complexes.